This invention relates generally to multilayer liquid absorption and deformation devices. More particularly, it relates to such devices for medical purposes and most particularly it relates to self-expandable intraluminal vascular stents employing such devices wherein the liquid is water.
In some embodiments, the stents may be biodegradable or they may be capable of releasing therapeutic drugs or they may be capable of doing both simultaneously.
Biodegradable and drug releasing stents and other medical devices are not new in the art as evidenced, for example, by the following patents: U.S. Pat. No. 5,306,250 to March et al. on Apr. 26, 1994; U.S. Pat. No. 5,443,458 to Eury et al. on Aug. 22, 1995; U.S. Pat. No. 5,443,495 to Buscemi et al. on Aug. 22, 1995; U.S. Pat. No. 5,464,450 to Buscemi et al. on Nov. 7, 1995; U.S. Pat. No. 5,500,013 to Buscemi et al. on Mar. 19, 1996 and Japanese patent application J63-9715 8 A, published Apr. 27, 1988.
U.S. Pat. No. 5,389,106 to Tower on Feb. 14, 1995 describes a stent having an impermeable polymer membrane disposed inside a wire frame. However, the membrane is not biodegradable.
Devices making use of water swellable material, some of which are stents, are described in U.S. Pat. No. 4,460,642 to Errede et al. on Jul. 17, 1984; U.S. Pat. No. 4,496,535 to Gould et al. on Jan. 29, 1985; U.S. Pat. No. 4,872,867 to Joh on Oct. 10, 1989; U.S. Pat. No. 5,163,952 to Froix on Nov. 17, 1992; U.S. Pat. No. 5,234,456 to Silvestrini on Aug. 10, 1993; U.S. Pat. No. 5,258,020 to Froix on Nov. 2, 1993; U.S. Pat. No. 5,464,419 to Glastra on Nov. 7, 1995; U.S. Pat. No. 5,554,180 to Turk on September 1996; EP patent 0502905B1 on Sep. 14, 1994 and EP patent 0441516B1 on Mar. 29, 1995. None of these patents make use of swellable material in the manner of this invention nor for the same purpose.
The content of all of the above-identified patents are incorporated herein by reference.
The basic concept of this invention is analogous in a general way to a bimetal. A bimetal comprises two metals bonded together that expand differently to undergo deflection. For example, the best known bimetal may be the type consisting of two thin strips of metal having different thermal expansion coefficients bonded together. Deflection or bending of such a structure is in response to temperature change. Such bimetals in the form of a beam, helical or spiral structure have been commonly used in temperature sensing devices such as thermostats and thermometers.
This invention on the other hand and in an analogous way combines two or more layers of material together in superimposed fashion in which at least two of the layers exhibit differential liquid absorbency. For example, a two layer structure in which one layer is hydrophilic and the other layer is not or which is less hydrophilic than the one layer will, upon exposure to water, analogously undergo deflection or bending because the absorption of water by the hydrophilic layer causes swelling of the layer. Since it is superimposed upon the other layer, deflection or bending results in a way analogous to the deflection of bimetal structures already described.
A beam-like structure may be used as an actuator or the like to respond or signify the presence of water or some other absorbable liquid.
The concept, as will be described in further detail hereinbelow, may be used in a variety of medical applications although not limited thereto, including self-expanding stents.